1. Field of the Invention
This invention relates to an apparatus for automatically feeding one or more documents to an image forming apparatus such as a copying machine, and more particularly to an automatic document feeding apparatus capable of continuously sending simplex or duplex original documents to a document reading station in the image forming apparatus with high efficiency in accordance with a desired document feeding mode by using a document feeding mechanism simple in structure and easy to control.
2. Description of the Prior Art
An automatic document feeder (ADF) has become to be applied for automatically sending one or more original documents in succession to a document reading station in an image forming apparatus such as a copying machine, facsimile and image scanner. Coping with a need which has been felt for high-speed image processing in the image forming apparatus as noted above, the automatic document feeder has been desired to operate at high speed. Furthermore, there has been a need for a small-sized and energy-saving document feeder.
For introducing automation into the document feeder, it is necessary to fulfill a function of handling not only a simplex document having information to be read out on its one side, but also a duplex document having information on its both sides. Conventional document feeders possessing such a function are disclosed in U.S. Pat. No. 5,280,330; U.S. Pat. No. 5,327,205; U.S. Pat. No. 5,377,966; U.S. Pat. No. 5,601,281; and Japanese Patent Application Public Disclosure No. HEI 6-263332(A).
For instance, the automatic document feeding apparatus disclosed in Japanese Patent Appln. Pub. Discl. No. HEI 6-263332(A) is composed of a lot of motion transmitting components including gears, timing belts, pulleys, levers, electromotive clutches and electromotive solenoids for transmitting the motive power generated by a single drive source (motor) to a drive means, and further employs a plurality of detecting elements such as a rotary encoder for observing the movement of the motion transmission components. Thus, the prior art document feeders ordinarily necessitate such complicated driving and controlling mechanisms consisting of the single drive source and many driving components including feeding rollers and powered actuators with electromotive clutches and electromotive solenoids, which must be operated and controlled with exquisite timing. It is a matter of course that the conventional document feeders are basically limited in their operation speed and complicated in structure.
In general, to feed the original documents from a document supply tray of the document feeder to a document reading station of the image forming apparatus, the original documents are sent out one by one from the document supply tray in such a manner that after the preceding document is read out at the document reading station and discharged therefrom, the following document starts from the document supply tray toward the document reading station. Consequently, until the following document from the document supply tray reaches the document reading station, the image forming apparatus is temporarily suspended to wait for the following document, resulting in a time loss. In an inefficient document feeder, until the preceding document subjected to image processing is completedly discharged from the document feeder, the feeder does not start to feed the following document, consequently to remarkably lengthen the intervals of time at which the original documents are sent out one by one from the document supply tray, and decrease the operation speed.
In a case of dealing with duplex documents, a process for inverting the document is required, resulting in decrease in operation speed and prolongation of the processing period.
In principle, even the conventional document feeder as noted above may possibly be operated at high speed by elevating the operation speed of the driving component elements. However, the speeding up of the operation of the component elements involves many problems such as occurrence of excessive inertia, degradation of performance and reliability, and production of noises.
There may be considered an idea such that during image processing for the preceding document at the document reading station, the following document is sent out from the document supply tray to be beforehand brought near the document reading station just after the preceding document processed goes out of the document reading station so as to replace the documents at the document reading station at a short interval of time. Nevertheless, the conventional document feeders as described above are not possessed of a mechanism capable of embodying the aforementioned idea for speeding up the document feeding operation.
Moreover, the document feeder for the image forming apparatus has been desired to offer a "2-in-1" function of reading out images on two original documents placed side by side on the document reading station at one time. To give one example of the 2-in-1 function, two original documents of A4 size are placed side by side on the document reading station and read out in one operation to obtain a copy of A3-size on which the images of the two original documents are reproduced or a reduced copy of A4 size to which the images copied from the original documents of A4 size are reduced. The 2-in-1 function contributes toward speeding up of the operation of the image forming apparatus, but could not easily be fulfilled by the conventional document feeding apparatuses.